Non-straight synthetic filaments, especially those made wavy by crimping or the like, have been made for a variety of purposes, e.g., for brush bristles of various types (e.g., see Cansler et al U.S. Pat. No. 5,161,555), but mostly for carpet and textile fibers in order to simulate natural fibers.
The conventional fiber crimping machine employs a pair of intermeshing gears with mating teeth or indentations. The gears are set at a fixed distance apart so that the teeth do not "bottom out", but rather a gap is maintained to accommodate the thickness of the synthetic fibers or monofilaments fed between the gears. If the fibers are of thermoplastic material, the gears may be heated to soften the fibers before or while they are between the meshing teeth. Such methods are described for example in the McCullough et al U.S. Pat. No. 4,979,274, which is herein incorporated by reference. This patent shows an apparatus which is adaptable for different fiber thicknesses by interchanging the crimping teeth (FIG. 2).
In the days when most paints were made with organic solvents (not water-based), natural hog bristles, which are both wavy and tapered, were used in the best and most expensive paint brushes, in spite of the fact that they wore out quickly. Natural hog bristles are less used now because water-based paints constitute about 90-95% of the paints on the market, and hog bristles are highly hygroscopic; if used with water-based paints they swell and the brush becomes unsatisfactory. Thus, synthetic bristles have largely replaced natural bristles, especially in paint brushes. Synthetic paint brush bristles outwear natural hog bristles by a factor as much as 10 to 1.
Non-wavy (e.g., uncrimped), synthetic tapered bristles are employed today in better synthetic paint brushes, and level (i.e., non-tapered), waved or wavy synthetic bristles are employed in specialty applicator brushes other than paint brushes, e.g., mascara and blusher brushes. The prior art does not teach or suggest forming or employing wavy, tapered, synthetic brush bristles in brushes of any type, including the preferred material-applicator brushes of this invention, and clearly does not teach or suggest forming or employing wavy, tapered synthetic brush bristles wherein the amplitude of the wave is substantially uniform.
U.S. Pat. No. 4,381,325 to Masuda et al. illustrates tapered filaments that are also slightly waved (e.g., FIGS. 9b and 9c) over a portion of their lengths; with the wave lacking a constant amplitude. Although the Masuda patent teaches at col. 6, lines 8-13 that crimped filaments can be employed in textile fabrics, if necessary, the Masuda patent also specifically teaches at col. 5, lines 54-58 that waved filaments should not be employed as brush bristles. Thus the Masuda patent teaches away from the present invention.
U.S. Pat. No. 2,508,799 to Reis shows brush bristles which are tapered, are of asymmetrical cross section, and have a changing cross section (see col. 4, line 46). No waving is disclosed. Also see Ward et al U.S. Pat. No. 4,307,478.
Costa, U.S. Pat. No. 4,365,642, shows bristle-like protuberances on a molded mascara applicator which appear to be tapered and also curved (FIGS. 2-6). However, the curves are too short--less than a complete cycle--to be classified as "waves" or to disclose any wave characteristics, including uniform amplitude.
Browne et al, U.S. Pat. No. 2,508,489, shows a crimping machine which adjusts to different thicknesses of fiber (col. 1, line 41). Crimping force is applied by a spring (col. 6, line 16).
The conventional crimping machines described above, which crimp fibers between intermeshing gear teeth with a constant clearance, are not satisfactory for producing uniform waviness in tapered bristles. It has been found that when tapered fibers are fed through such a conventional machine, the thicker ends of the fibers come out more wavy (i.e., with a greater amplitude) than the thinner ends. Insofar as is known, no solution to this problem has been found previously.
In addition to the fact that those skilled in the art did not know how to produce a wavy and tapered bristle, it also has been thought that, even if crimped and tapered bristles could be achieved, brush bristles, and in particular a paint brush formed from such bristles might not be satisfactory because it would be too bulky, the waves might interfere with traditional brush making techniques, or the paint brush might look different and not be acceptable to consumers. This prior art thinking is reflected in the earlier-discussed Masuda '325 patent, which specifically teaches that even the partially waved filaments disclosed therein should not be used for brushes of any type, including paint brushes.